Open loop and closed loop amplifiers are known. It is generally known that a feedback circuit (i.e., feedback loop) surrounding an amplifier (i.e., surrounding an otherwise an open loop amplifier) can be used to set a gain of a resulting closed loop amplifier to a desired closed loop gain determined by a few passive circuit components, for example, a few resistors. Closed loop amplifier arrangements, compared with open loop amplifiers, tend to have less change of gain (i.e., closed loop gain) due to a variety of undesirable changes and variations, for example, changes in temperature and unit to unit variations.
Some closed loop amplifiers have one or more passive circuit components (e.g., resistors) within a feedback circuit. Some other closed loop amplifiers have one or more active circuit components within a feedback circuit. In those arrangements that use and active circuit component in a feedback loop, a gain of the resulting closed loop amplifier can be, at least in part, dependent upon a characteristic of the one or more active circuit components, for example, a resistance of the one or more active circuit components. It is known that some active circuit components have a resistance that varies with a power supply voltage used to power the one or more active circuit components. Thus, the closed loop gain of such a closed loop amplifier can vary with respect to power supply voltage.
In order to counter the undesirable change of closed loop gain with respect power supply voltage, some existing closed loop amplifiers that use one or more active circuit components within the feedback circuit use a regulated power supply to power the one or more active circuit components.
A voltage regulator tends to take up silicon real estate and increase integrated circuit cost, and is therefore undesirable. A voltage regulator also tends to consume power.
It would be desirable to provide a closed loop amplifier that has one or more active circuit components in a feedback circuit and that has a reduced undesirable change of closed loop gain, that can result, for example, from an undesirable change of resistance of the one or more active circuit components with respect to a power supply voltage used to power the one or more active circuit components.
In some arrangements, it would also be desirable to provide a circuit that can achieve a stable and consistent ratiometry between two circuit characteristics.